1. Technical Field
The present disclosure relates generally to wireless communications and, more particularly, to noise cancellation in a receiver front-end.
2. Description of Related Art
The wide adoption of wireless communication standards has created a crowded radio frequency (RF) spectrum with unprecedented levels of interference. For example, a radio receiver receiving a wanted signal must often contend with relatively large and unwanted signals on nearby frequencies (e.g., adjacent channels). These signals are often referred to as “blocking signals” or “blockers”, and are known to cause issues such as gain compression in a receiver. Interference problems may be exacerbated when multiple radios are integrated in a single device, leading to “coexistence” blockers.
In addition, during down-conversion in a receiver, reciprocal mixing of the phase noise of a local oscillator (LO) with an unwanted blocker may deposit additive noise, proportional to the blocker amplitude, on top of a desired signal. Receiver desensitization due to reciprocal mixing can be mitigated, in some instances, by filtering unwanted blocking signals prior to down-conversion using fixed radio frequency (RF) bandpass filters placed immediately after the antenna. Such filters are expensive, require discrete filtering components, and, generally, are undesirable in certain applications, such as true Software-Defined-Radios (SDRs) that require wide bandwidth operation.
The undesirable effects of reciprocal mixing may also be mitigated by implementing local oscillators that have relatively minimal phase noise, such as LC-oscillators utilizing integrated resonators. However, the phase noise improvement provided by an LC-oscillator comes at the expense of increased power dissipation, the requirement of an integrated inductor, and other design trade-offs.